<a class="navbar-brand" href="#">Navbar</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarsExampleDefault" aria-controls="navbarsExampleDefault" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
</button>

<div class="collapse navbar-collapse" id="navbarsExampleDefault">
    <ul class="navbar-nav mr-auto">
        <li class="nav-item active">
            <a class="nav-link" href="/">Home <span class="sr-only">(current)</span></a>
        </li>
        <li class="nav-item">
            <a class="nav-link" href="/task/list">Task</a>
        </li>
        <li class="nav-item">
            <a class="nav-link disabled" href="#">Disabled</a>
        </li>
        <li class="nav-item dropdown">
            <a class="nav-link dropdown-toggle" href="#" id="dropdown01" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">Dropdown</a>
            <div class="dropdown-menu" aria-labelledby="dropdown01">
                <a class="dropdown-item" href="#">Action</a>
                <a class="dropdown-item" href="#">Another action</a>
                <a class="dropdown-item" href="#">Something else here</a>
            </div>
        </li>
    </ul>
</div>